The present invention relates to a hydration modifier for mortar or concrete making it possible to obtain a limited shrinkage, to a Portland-type dry cement composition, to a ready-to-use concrete composition, to the process for preparing a mortar or concrete composition, to the use of the mortar or concrete compositions for the manufacture of construction works and to the self-leveling screeds manufactured from the mortar or concrete compositions.
In general, in order to compensate for the shrinkage of building works, it is common practice to use non-shrink admixtures which make it possible to obtain an expansive process for mortars or concretes. Among these admixtures, mention may be made, for example, of micronized aluminum powder, calcium carbide, quick lime, hydrogen peroxide, calcium sulfate, calcium aluminosulfate and iron powder. The swelling obtained with these non-shrink admixtures is of the order of 300 to 800 xcexcm per meter after 28 days. The shrinkage of the cement/aggregate mix being of the same order of magnitude: 600 xcexcm per meter for a mortar normalized after 28 days.
In theory, the shrinkage is therefore well compensated for, but in fact it is very difficult to control this expansion as well as the moment that it occurs.
It therefore appears important to develop a ready-to-use mortar or concrete composition which does not have these problems of controlling the expansion.
The applicant has surprisingly discovered, by turning toward a technology other than that normally employed in the field, that a mortar or concrete composition which comprises a Portland-type cement in combination with a hydration modifier produces a modified microstructure that does not lead to significant swelling during setting and limits the shrinkage during drying of the cementitious matrix of the mortar or of the concrete.
This is because the applicant noticed on the one hand that by combining at least one Portland-type cement with a modifier comprising at least three ingredients in proportions defined below, it obtained a mortar or concrete with limited shrinkage.
On the other hand, it noticed that the ingredients constituting the hydration modifier, in the proportions indicated, themselves have a synergistic action on the non-shrink effect of the Portland-type mortars or concrete.
A first subject according to the invention is a hydration modifier for mortar and concrete, comprising, in combination, from 30 to 80% of calcium sulfate, from 3 to 60% of ethylene oxide/propylene copolymer and from 0.5 to 6% of activator for the copolymer.
The calcium sulfate may be used in the form of gypsum or in anhydrous form, but in a preferred embodiment according to the invention it will be used in anhydrous form.
The ethylene oxide/propylene copolymer is a copolymer capable of being activated by the addition of an activator or catalyst. It will be possible to use copolymers differently substituted in terms of ethylene and propylene, but in a preferred embodiment copolymers consisting of 60 to 90% of ethylene oxide will be used.
The activator or catalyst makes it possible to activate the ethylene oxide/propylene copolymer used and may be any type of suitable activator. In a preferred embodiment, imidazole may be used as the activator for the ethylene/propylene [sic] copolymer.
In an even more preferred embodiment according to the invention, the hydration modifier comprises 51% of calcium sulfate, 46% of ethylene oxide/propylene copolymer and 3% of imidazole.
In another even more preferred embodiment according to the invention, the modifier comprises 80% of calcium sulfate, 18% of ethylene oxide/propylene copolymer and 2% of imidazole.
A second subject according to the invention is a ready-to-mix Portland-type dry cement composition comprising from 2to 10% by weight of a hydration modifier according to the first subject of the invention.
The Portland-type cement may be chosen from pure or compound cements.
In a preferred embodiment according to the invention, the cement composition comprises from 4 to 6% by weight of a hydration modifier.
A third subject according to the invention is a ready-to-use mortar or concrete composition comprising from 0.5 to 2.5% by weight of a hydration modifier, according to the first subject of the invention, in combination with a Portland-type cement.
In a preferred embodiment according to the invention, the mortar or concrete composition comprises from 0.8 to 1.3% by weight of a hydration modifier.
The mortar or concrete compositions according to the invention may include other admixtures, known per se in the art, of the type mentioned below.
For example, mention may be made of admixtures which act on the setting and hardening time, such as, especially, accelerators which shorten the time between hydration of the binders and their setting, and retarders which extend the time between the hydration of the particles of a binder and the onset of its setting. As accelerators, mention may be made, for example, of calcium or sodium chlorides, certain alkalis (soda, potash, ammonia) or their salts (potassium or sodium sulfate) . As retarders, mention may be made of carbohydrates (sugars, glucose, starch, cellulose), various acids or acid salts, or else zinc oxide or alkali phosphates.
Mention may also be made of admixtures which act on the plasticity and the compactness, such as plasticizers, thinning agents, called water reducers, air entrainers and thickeners. As plasticizers, bentonite, fat lime, ground limestone, flyash and keiselguhr may, for example, be incorporated. As thinning agents, naphthalene sulfonate, lignosulfates, sulfonated melanine [sic], resin soaps or synthetic detergents may be used. As air entrainers, sulfonates, sodium abietate or alkaline soaps of fatty acids may, for example, be used. As thickeners or antisedimentation stabilizers, methylcellulose, silica fume, stabilized casein and biopolymers may be mentioned.
Mention may also be made of admixtures which improve the resistance to external agents, such as antifreezing agents, which protect the material from the effects of frost until it has hardened; frost-preventing agents, which protect the hardened concretes from the effects of frost; waterproofing agents, which improve the impermeability of the concretes by reducing the possibilities of water penetrating by capillary effect; cure products, which prevent premature evaporation of the mixing water and maintain the necessary hydration. As antifreezing agents, calcium chloride or sodium aluminate may, for example, be used. As frost-preventing agents, air entrainers may be used. As waterproofing agents, silicones, fluosilicates, colloids or resins may be used. As cure products, emulsions of paraffins or waxes, oils, resins and various petroleum derivatives may, for example, be used.
The admixtures will be added in small proportions and must conform to the French standard NF P 18-103.
Depending on the season and/or the distance from the worksite to the place of manufacture, it will be possible, for example, to add superplasticizer-type rheology agents and antisedimentation agents to the mortar or concrete composition according to the invention.
The mortar or concrete compositions, so as to have a self-leveling character, may furthermore include one or more plasticizers, thinning agents, thickener and/or air entrainer.
This list is not exhaustive and the formulation of the mortar or concrete composition may be completed by adhesion promoters and antifoam agents.
In a preferred embodiment according to the invention, the mortar or concrete composition with a self-leveling character furthermore includes from 1 to 5% by weight of a thinning agent with respect to the weight of cement.
The mortar thus obtained may be pumped and spreads by itself. All that is required is to respect the levels to be attained and to carry out an outgassing operation. The building work thus constructed, such as a screed, presents the same ease of implementation as a self-leveling screed of the calcium-sulfate type, but with water insensitivity and the ability to bond to tiles in very short times. It is therefore possible to cast outdoors, and resistance to moisture penetration is obtained.
A fourth subject according to the invention is a process for preparing a mortar or concrete composition according to the invention, comprising the introduction of the hydration modifier either during the manufacture of the cement or during the mixing, after the mortar or concrete composition has been mixed.
A fifth subject according to the invention is the use of a mortar or concrete composition according to the invention for the manufacture of construction elements in the field of buildings, roads and airports, and, for example, for the manufacture of waterproofing mortars or impermeable concretes.
In a preferred embodiment according to the invention, a mortar or concrete composition with a self-leveling character according to the invention is used, for the manufacture in the field of floors [sic], and more particularly of screeds.
Finally, a sixth subject according to the invention is a self-leveling screed manufactured from a mortar or concrete composition with a self-leveling character.
The advantage of the screeds according to the invention, manufactured from mortar or concrete compositions with a self-leveling character according to the invention, is that there is no risk of secondary crystallization of the ettringitic nature at the screed/tiling interface or screed/concrete substrate interface. In addition, it is not necessary, as in the case of calcium-sulfate-based screeds, to use primer-type layers for isolating the adhesive from the cast substrate.
FIG. 1 shows the shrinkage of a cement, depending on the composition of the hydration modifier in the Portland-type cement (68% of calcium sulfate, 30% of ethylene/propylene [sic] copolymer and 2% of imidazole).
The control contains no hydration modifier.
Anhydrite means anhydrous calcium sulfate.
CoPol means ethylene oxide/propylene copolymer.
Imid means imidazol.
The shrinkage results, depending on the ingredient or ingredients or constituents added, are iven in the following table.
It is clearly apparent that the combination of calcium sulfate, ethylene/propylene [sic] copolymer and imidazole makes it possible to obtain a synergistic effect on the shrinkage of the cement.
The examples which follow are used to illustrate the invention, but in no way constitute a limitation to the scope of the appended claims. TEST METHODOLOGY:
1xe2x80x94Laboratory tests:
a) mixing procedure: this is carried out in accordance with the provisions of the EN 196-1 standard. The constituents (sand, cement, additive and water) are introduced in the following ratios:
Sand/Cement ratio=3
Modifier/Cement ratio=0.053
Water/Cement (W/C) ratio=0.50.
After the standardized cycle, the modifier is introduced, this being followed by high-speed mixing for 4 minutes;
b) forming the test specimens: the mortar coming from mixing is put into the shrinkage molds, having dimensions of 4xc3x974xc3x9716 cm or 7xc3x977xc3x9749 cm, the molds being equipped with shrinkage blocks according to the NF P 15-433 standard. In the case of self-leveling mortars, they are formed as a single course, without vibration;
c) storage conditions:
After mixing, the molds are stored in a wet atmosphere at 95% relative humidity and 20xc2x0 C. After 24 h, the test specimens are then stored in the laboratory atmosphere at 20xc2x0 C. and 50% relative humidity until 48 hours have elapsed;
d) measurement conditions
For reasons of comparison with the worksite controls, the measurements of which start after 48 h, the initial measurement of the laboratory tests takes place under the same conditions.
2xe2x80x94Worksite tests:
a) Production of the test specimens: the mortar coming from mixing in the concrete mixer is put into the shrinkage molds, having dimensions of 7xc3x977xc3x9749 cm or 7xc3x977xc3x9728 cm, these being equipped with shrinkage blocks. The self-leveling mortars are laid as a single course, without vibration. The test specimens are stored on the worksite until 24 h of hardening, with a device preventing premature evaporation during setting. After 24 h, the test specimens are moved to the measurement laboratory.
b) Measurement conditions: the initial measurement is carried out after 48 h.